Blood products, especially those intended for transfusion, are non-homogeneous in that they include several cell types as well as a variety of molecular components having differing biological activities. Often patients into whom the blood is to be transfused are only in need of one component (e.g. red blood cells for gas transport), and the other components present in the blood product are not only unnecessary but may even be disadvantageous or harmful.
In particular, in the field of autologous transfusion, when the patient's own blood is recovered before, during or after surgery and is purified before being returned to the same individual, the recovery of autologous blood presents a technical challenge. Autologous transfusion is beneficial from a medical standpoint because many of the epidemiological and immunological problems associated with the use of donor blood are avoided. However, in such procedures as open heart surgery, a significant volume of the patient's blood (1 to 3 liters) is in the extracorporeal circuit associated with heart-lung machines. This blood is diluted with crystalloid solutions used to prime the machine, is heavily anticoagulated with heparin to prevent clot formation, and contains free hemoglobin and potassium derived from red blood cells damaged during the surgical procedure. To use this blood for autologous transfusion, the unwanted constituents (water, heparin, free hemoglobin and potassium) must be removed. In other intra-operative blood recovery procedures, such as in thoracic and orthopedic surgery, the patient's blood is typically suctioned from the open wound and subjected to cleansing procedures. The blood salvaged in this manner is considerably more contaminated than that recovered from heart-lung machines, since it contains fragments of tissues generated by surgery, in addition to the contaminants mentioned above.
Currently, two techniques are used to remove contaminants: the first relies upon washing fluids and associated equipment such as centrifuges. In addition to the mechanical complexity of a system that involves centrifuging, this technique requires the addition of buffer solutions that must then be removed, and it provides red blood cell (RBC) fractions depleted of all plasma proteins. The second, which is based on depth dead-end filtration, may be broadly divided into two classes: blood sieves and blood component filters. Blood sieves are very coarse in pore size and have a strong tendency to block quickly if the pore size is finer than a minimum. They are used primarily for removing large particles such as bone chips, tissue fragments, agglomerates and the like from blood. Blood component filters are used primarily for removing selected natural blood components such as leukocytes. They are incapable of removing small molecules such as hemoglobin.
In addition to surgical transfusion with autologous blood, a second major utility for a blood filter that could remove small molecules is found in the reconstitution of stored blood. One of the methods commonly used for the preservation of packed red blood cells is storage of the frozen cells at -80.degree. C. The process involves the addition of cryoprotectant agents (commonly glycerine), freezing the cells, thawing, and finally washing the cells to remove the cryoprotectant. The freezing and thawing cause lysis of the red cells and the release of free hemoglobin.
Free hemoglobin in whole blood and blood fractions is undesirable due to its toxicity, a particularly severe complication being renal toxicity. Thus, it would be advantageous to have a device and method to remove free hemoglobin from whole blood and blood fractions.
It is known that hemoglobin can be obtained from solution by affinity chromatography. For example, U.S. Pat. No. 4,925,574 to Hsia describes an agarose gel to which are attached various hemoglobin ligands for affinity chromatography. This appears to be a useful technique when obtaining hemoglobin is the object, but it cannot be used to remove hemoglobin from whole blood or blood fractions when obtaining the blood is the object because (a) gels are mechanically unstable, (b) gels are impenetrable to cellular components and (c) many gel substrates induce lysis and release of hemoglobin (see below).
It would therefore be highly desirable to have a method for removing hemoglobin along with other debris from whole blood or blood fractions quickly and efficiently.